A variety of antibacterial pyridonecarboxylic acid derivatives are known. For example, Japanese Patent Application Laid-Open No. 56673/'89 describes pyridonecarboxylic acids of the general formula ##STR2## wherein R represents a lower alkyl group, a halogenated lower alkyl group, a lower alkenyl group, a cycloalkyl group, or a phenyl group which may have one or more substituents; X represents a nitrogen atom or C--A in which A represents a hydrogen atom or a halogen atom; Y represents a hydrogen atom or a halogen atom; and Z represents a group of the formula ##STR3## in which R.sub.1 represents a hydrogen atom, a lower alkyloxycarbonyl group, or an acyl group that may be substituted by one or more halogen atoms; two of R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are connected directly or through a lower alkyl chain to form a ring, and the others represent hydrogen atoms; and n is 0 or 1, provided that R.sub.25 and R.sub.3 are directly connected. However, no specific example of a compound of the above formula (A) in which R.sub.4 and R.sub.5 are connected through an ethylene chain to form a ring is disclosed therein.
Moreover, European Patent Application Laid-Open No. 0343524 discloses pyridonecarboxylic acid derivatives of the general formula ##STR4## wherein R.sub.1 is hydrogen, hydroxy, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, oxo, halogen, or amino which may optionally be substituted by C.sub.1 -C.sub.4 alkyl and/or C.sub.1 -C.sub.4 alkanoyl; R.sub.2 is azido, hydroxy, C.sub.1 -C.sub.4 alkoxy, C.sub.1 -C.sub.4 alkoxycarbonyl, C.sub.1 -C.sub.4 alkanoyl, or amino which may optionally be substituted by C.sub.1 -C.sub.4 alkyl and/or C.sub.1 -C.sub.4 alkanoyl: A is ##STR5## R.sub.3 is hydrogen or a carboxyl-protecting group; R.sub.4 is C.sub.1 -C.sub.4 alkyl, C.sub.2 -C.sub.5 alkenyl, C.sub.3 -C.sub.5 cycloalkyl, mono- or difluorophenyl, or a five-membered or six-membered heterocyclic group which may optionally be substituted by halogen and/or C.sub.1 -C.sub.4 alkyl; R.sub.5 is hydrogen, amino, hydroxy or C.sub.1 -C.sub.4 alkoxy; R.sub.6 is halogen: X is CH-(C.sub.1 --C.sub.4 alkyl), C.dbd.CH.sub.2, N--H or N--(C.sub.1 -C.sub.4 alkyl); Z is CQ or N; Q is hydrogen, C.sub.1 -C.sub.4 alkoxy, halogen, C.sub.1 -C.sub.4 alkyl or cyano; m is an integer of 0 or 1; and n and p are each an integer of 1 to 3. However, they do not include any compound in which n is 0.
Furthermore, Chemical Abstract, 66, 37500b (1967) and Japanese Patent Application Laid-Open No. 11729/'81 disclose compounds of the formula ##STR6## wherein R represents a hydrogen atom or a carboxyl group.
Conventional pyridonecarboxylic acid derivatives substituted by a bicyclic amino group, such as those represented by the above general formulae (A) and (B), are useful as antibacterial agents. However, their antibacterial activities and, in particular, in vivo antibacterial activities are not always satisfactory.
The present invention has been completed as a result of extensive investigations conducted with a view to developing a pyridonecarboxylic acid derivative showing a further enhancement in antibacterial activity and, in particular, in vivo antibacterial activity.